1. Field of the Invention
The present invention relates to an apparatus and a method for measuring gas or liquid flow rate according to the preambles of the independent claims. More particularly, the present invention discloses the design and manufacturing of comprising components of a thermal flow meter with a working principle based on time-of-flight methodology which can provide a flow speed measurement regardless the composition of flow media.
2. Description of the Related Art
Various gas or liquid flow meters with different working principles have been heretofore developed and commercially available on market. The gas and liquid flow meters are broadly deployed in various gas control and monitoring industries such as chemical, food process, beverage, medical, pharmaceutical, and utility gas applications. Among various technologies, however, most of the measuring technologies are very limited to the consistency of its flow media contents and composition.
The thermal flow sensing technologies can be classified into three categories in terms of the working principle: (a) anemometric, (b) calorimetric, and (c) time-of-fight (TOF). The first two methodologies measure the amount of heat that has been carried away by the flow media in a direct or indirect way. The amount of the heat that had been carried away is directly proportional to the flow speed as well as the mass of the fluid and hence these two methodologies provide the direct mass flow measurement. For thermal time-of-flight flow sensing technology, however, it measures the time span for heat wave that is carried away by the flow fluid to travel from upstream of heater position to the downstream sensing element position. The lower the flow speed is, the longer time it takes for the heat wave to travel which will benefit to develop a better signal process capability. This character is then entirely superior to the other two thermal flow sensing principles; therefore it suggests that time-of-flight would be more beneficial on low flow range measurement and can be combined with the other two technologies to increase the dynamic range of entire flow measurement. This combination would particular useful as the time-of-flight can provide a composition-independent measurement while the other two can provide the direct mass flow information. In addition, time-of-flight approach could be an ideal method for the applications where the fluidic composition varies during measurement, such as city natural gas metering and human respiratory machines.
Therewith, the current invention shall have properties in many aspects of differentiation include dynamic metrology capability, faster response, lengthy lifetime, easiness of integration and lower cost.